Sigmodontinae incertae sedis. Genus diagnosed to encompass another problematic thomasomyine-like species from the Atlantic Forest region; see Osgood (1933b) and Pine (1980b) for historical reviews of the generic affiliations of the type species. The categorical recognition of this taxon, conventionally treated as a subgenus of Thomasomys (e.g., Carleton and Musser, 1984; Corbet and Hill, 1991; Pine, 1980b), will depend on phylogenetic studies involving other SE Brazilian endemics (also see comments under Delomys and Juliomys).